1. Field of the Invention
The invention relates generally to an electronic dimmer for dimming the brightness of a lamp and, more particularly, the invention relates to an electronic dimmer that uses analog and burst dimming to control the brightness of a lamp.
2. Description of the Related Technology
Typically, a liquid crystal display (LCD) backlight inverter uses analog and burst dimming to control the brightness of a cold cathode fluorescent lamp (CCFL), which is generally used to provide backlight illumination. Generally speaking, analog dimming techniques use an error amplifier that compares a reference or dimming control voltage to a voltage representative of lamp current to control the brightness of the lamp. On the other hand, burst dimming techniques may use a duty-cycle modulated output signal having a frequency in the range of about 200 Hertz (Hz) to about 100 kilohertz (kHz) to control the brightness of a lamp.
In some cases, burst dimming may be used in combination with analog dimming because analog dimming does not effectively control the brightness of a lamp from zero to one hundred percent. Unfortunately, conventional integrated circuits that provide a combination of analog and burst dimming control capability require two pins to perform these functions (i.e., one pin for each of the analog and burst dimming functions).
In accordance with one aspect of the invention, an electronic dimmer includes a main switch controller for receiving a sawtooth waveform having a predetermined frequency and an amplitude and for receiving a voltage signal having a maximum value greater than the amplitude. The voltage signal may be received via a dimming terminal and the main switch controller may be adapted to generate a burst dimming signal for use in controlling a switch by comparing the voltage signal with the sawtooth waveform. The electronic dimmer may also include a current supply starter for generating a current supply starting signal when the voltage signal is greater than the maximum value and a current source for supplying a current for varying a reference voltage according to the current supply starting signal. The electronic dimmer may further include a reference voltage generator for generating a reference voltage when substantially no current is provided via the current source. The reference voltage generator may be adapted to vary the reference voltage based on the current supplied by the current source. Additionally, the electronic dimmer may include a feedback unit for comparing the reference voltage to a voltage generated by a load current and for varying the brightness of a lamp based on the reference voltage.
In accordance with another aspect of the invention, an electronic dimmer includes an integrated circuit substrate and a burst dimmer circuit formed on the integrated circuit substrate. The burst dimmer circuit may be adapted to control the illumination intensity of a lamp over a first operating range. The electronic dimmer may also include an analog dimmer circuit formed on the integrated circuit substrate adjacent to the burst dimmer circuit, and the analog dimmer circuit may be adapted to control the illumination intensity of the lamp over a second operating range that overlaps the first operating range. Additionally, the electronic dimmer may include a plurality of electrical contacts, each of which is electrically coupled to one of the burst dimmer and analog dimmer circuits and one of which provides a dimming control voltage to both of the burst dimmer and analog dimmer circuits.
The invention itself, together with further objectives and attendant advantages, will best be understood by reference to the following detailed description, taken in conjunction with the accompanying drawings and the appended claims.